diff --git a/adr/authors.yml b/adr/authors.yml
index 62714d4..e7b1f3a 100644
--- a/adr/authors.yml
+++ b/adr/authors.yml
@@ -3,4 +3,10 @@ Nicolae Nicora:
   title: OpenKCM Contributor
   url: https://github.com/nnicora
   socials:
-    github: nnicora
\ No newline at end of file
+    github: nnicora
+Chris Burkert:
+  name: Chris Burkert
+  title: OpenKCM Contributor
+  url: https://github.com/cb80
+  socials:
+    github: cb80
diff --git a/adr/tenant-id.md b/adr/tenant-id.md
new file mode 100644
index 0000000..fa9eb57
--- /dev/null
+++ b/adr/tenant-id.md
@@ -0,0 +1,50 @@
+# ADR-104: Tenant ID
+
+| Status | Date | Document Type |
+| :--- | :--- | :--- |
+| **Active** | 2026-03-05 | Architecture Design Record |
+
+## Context
+
+We define the following qualities for IDs of OpenKCM tenants:
+1. they MUST be globally unique
+1. they MUST be eternal, i.e. they can never be reused
+1. they SHOULD be opaque
+1. they MUST remain stable on tenant moves
+
+Besides that we define the following schema for IDs of OpenKCM tenants:
+1. Maximum length: 40 characters
+1. Allowed characters follow the URI unreserved characters spec:
+
+   `ALPHA / DIGIT / "-" / "." / "_" / "~"`
+
+We recommend to use a UUID in the standard lower-case format
+with dashes as specified in RFC 4122. Example:
+`658b416d-1f4a-41d9-b70c-59a2442b0724`
+
+Optionally this may be prefixed with a short literal string to easily
+grasp the semantic of it. Example:
+`kcm-658b416d-1f4a-41d9-b70c-59a2442b0724`
+
+## Decision
+
+We decide that tenant IDs must comply to the above mentioned restrictions.
+
+## Consequences
+
+### Positive (Pros)
+* Tenant IDs are globally unique, which prevents collision e.g. when moving a tenant
+* Tenant IDs are eternal, which clearly maps information over time
+* Tenant IDs are opaque, which decouples the ID from the internal structure
+  and prevents exposure of internal information
+* Tenant IDs are stable, which for example allowes the move of the whole tenant
+  between regions
+* Tenant IDs can be technically validated
+* Tenant IDs can be used in URIs
+* Attacks using very long tenant IDs can be mitigated
+
+### Negative (Cons) & Mitigations
+* Tenant IDs are restricted to the above rules, which may prevent other valid formats
+
+## References
+* [RFC 4122 - A Universally Unique IDentifier (UUID) URN Namespace](https://www.rfc-editor.org/rfc/rfc4122)